This invention relates to unsaturated polyester compositions which are quickly curable and capable of providing superior surface quality to molded products obtainable therefrom which are useful particularly as exterior body panels and other externally mounted parts of automobiles.
Fiber-reinforced plastics (FRP) using unsaturated polyester resins have superior characteristics not only regarding strength, heat-resistance, water-resistance and resistance against chemicals but also regarding productivity and are used extensively for bathtubs, water tank panels and bathroom sinks. Recently, unsaturated polyester sheet molding compound (SMC) and bulk molding compound (BMC) are becoming recognized as plastic materials for exterior body panels of automobiles and are beginning to be used not only for main exterior panels such as engine hoods, roofs and trunk lids, but also for other exterior parts such as spoilers, air-intakes and rocker panels. In the case of using SMC for exterior body panels of automobiles, high surface quality, ability to be speedily curable and high productivity are particularly required of a sheet molding compound. If the curing speed of SMC can be increased even by seconds, for example, this alone can improve productivity significantly. For this reason, there have been several proposals for quick cure catalysts (such as U.S. Pat. No. 4,278,558), but surface smoothness of SMC tends to be sacrificed if its curability is increased. It has been known to use polymethyl methacrylate, polyvinyl acetate, styrene-butadiene block copolymers, lactone-conjugated diene copolymers, etc. to improve surface smoothness of SMC products (for example, Japanese Patent Publication Tokkai No. 52-148588 and U.S. Pat. No. 4,287,313). Although surface smoothness of SMC products can be improved by using such low profile additives (modifiers), their surface quality is not sufficiently satisfactory even with additives if the curing speed is increased.